Diagnostic test elements are important components of clinically relevant methods for determining an analyte presence or concentration. An example of such methods is a rapid and precise enzyme-based determination of analyte concentration. In this manner, the analyte to be determined is contacted with a suitable enzyme, a coenzyme and optionally a mediator, where the coenzyme is physicochemically changed (e.g., oxidized or reduced) and subsequently detected by suitable methods.
When a mediator is used, it transfers redox equivalents released during enzymatic conversion of the analyte from the physicochemically changed coenzyme to an optical indicator or conductive components of an electrode for photometric or electrochemical detection, respectively. A calibration of a measured value then yields a direct relationship with the analyte concentration to be determined.
Mediators are known for use in test elements to determine analyte concentration and include, for example, potassium hexacyanoferrate, ferrocene derivatives, quinones, oxazines, phenazines and thiazines. A review of mediators that directly transfer redox equivalents to a suitable detection system and that can be used for electrochemically determining blood glucose may be found in, for example, Takaminami (2008) Mater. Integr. 21:317-323 and Heller et al. (2008) Chem. Rev. 108:2482-2505.
Other mediators can nitrosoanilines, such as those disclosed in U.S. Pat. Nos. 5,206,147 and 5,286,362. When compared to the mediators described above that enable a direct transfer of redox equivalents, nitrosoanilines are characterized in that firstly a precursor compound of the actual mediator is prepared, which then is reduced to the effective mediator that has an advantage of avoiding blank reactions.
A problem, however, when using nitrosoanilines is that they tend to form azoxy dimers and to have a high reactivity towards substances containing amino groups and mercapto groups. See, e.g., Hinson (1986) Adv. Exp. Med. Biol. 197:691-696). Use of nitrosoanilines thus can lead to undesired side reactions and adversely affect the specificity and sensitivity of the analyte concentration determination.
For the foregoing reasons, there is a need for mediators that lack the disadvantages noted above.